OVER a billion people live in tropical and subtropical areas where malaria is still a serious threat.1,2 The global eradication program has so far succeeded mostly in temperate zones. Resourceful mosquito vectors, through either physiological or behavioral resistance to residual insecticides, together with serious administrative problems, threaten the success of the eradication program.3 The appearance of chloroquine-resistant strains of falciparum malaria in South America and in Southeast Asia compounds the situation.4-9

Studies in volunteers in the United States, with strict controls, provide confirmation of drug resistance.8 Most of these strains are refractory not only to chloroquine, but to other synthetic antimalarials such as quinacrine (Atabrine), chlorguanide, and pyrimethamine.10

In late 1965, outbreaks of falciparum malaria appeared in American, Australian, and Korean troops in South Vietnam. Cases occurred almost exclusively among members of rifle companies who had engaged the Viet Cong in intense combat in the central high-land jungles. Clinical